How does the store manage complaints from the customers?

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I just want to know how does the store manage the complaints they received from the customers? Once, I have bad experience with Taco Bell. They server got mad at me for asking if I can extra spicy sauce, and an extra straw. He gave me a face that seems unpleasant to serve me with his mumbling words. I just complained to his manager at the fast food. Another time is with pep boys. I brought in my car for oil change and tire rotation. They had me wait for 2 hours there; and there were only 2 customers literally waiting there too. The mechanics back there just smoking and chatting on the cells. We ask why we have to wait that long; they receptionist just gave us attitude and disgusting manner. We had to file a complaint to the region manager on scene. In general, I just wonder how they manage those complaints? They just shrug their shoulders off, or would they do a monthly review on the performance of their employees?